PARIS, Feb 15 (Reuters) - France's military operation in the Central African Republic will last longer than initially planned because the situation in the country is worse than anticipated, French Defence Minister Jean-Yves Le Drian said on Saturday.

"I think it will be longer than expected because the level of hatred and violence is more important than we had imagined," Le Drian told France Inter radio.

"A military operation is not decreed as clockwork, we have to adapt."

France said on Friday it would send another 400 troops to help combat the crisis in the African country as U.N. chief Ban Ki-moon pleaded for more swift, robust international help to stop sectarian violence that could turn into a genocide.

Almost a million people, or a quarter of the population of the former French colony, have been displaced by fighting which erupted after the mostly Muslim Seleka rebel group seized power in March last year in the majority Christian country.

Seleka leader Michel Djotodia gave up power last month as Christian militias stepped up their attacks on Muslims.

At least 2,000 people have been killed since December in what a U.N. official described as a wave of "ethnic-religious cleansing".

France had hoped to quickly hand sole responsibility for security to the African Union peacekeeping force MISCA, which has deployed over 5,300 troops to Central African Republic, including soldiers from Rwanda, Burundi, Chad and Cameroon.

Earlier this month, Le Drian had said the United Nations would probably have to renew a mandate for French troops to restore order in Central African Republic when it expires in May because of continued violence there. (Reporting by Sybille de La Hamaide; Editing by Sophie Hares)